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<title>Chapter 8. The Conversion Library 1.7</title>
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<div><h2 class="title">
<a name="conversion"></a>Chapter 8. The Conversion Library 1.7</h2></div>
<div><div class="authorgroup">
<div class="author"><h3 class="author">
<span class="firstname">Bjarne</span> <span class="surname">Stroustrup</span>
</h3></div>
<div class="author"><h3 class="author">
<span class="firstname">Dave</span> <span class="surname">Abrahams</span>
</h3></div>
<div class="author"><h3 class="author">
<span class="firstname">Boris</span> <span class="surname">Rasin</span>
</h3></div>
<div class="author"><h3 class="author">
<span class="firstname">Antony</span> <span class="surname">Polukhin</span>
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<div><p class="copyright">Copyright © 2001 Beman Dawes</p></div>
<div><p class="copyright">Copyright © 2014-2025 Antony Polukhin</p></div>
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<a name="conversion.legal"></a><p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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<div class="toc">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="conversion.html#conversion.description">Description</a></span></dt>
<dt><span class="section"><a href="conversion/polymorphic_casts.html">Polymorphic casts</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="conversion/polymorphic_casts.html#conversion.polymorphic_casts.polymorphic_downcast">polymorphic_downcast</a></span></dt>
<dt><span class="section"><a href="conversion/polymorphic_casts.html#conversion.polymorphic_casts.polymorphic_cast">polymorphic_cast</a></span></dt>
<dt><span class="section"><a href="conversion/polymorphic_casts.html#conversion.polymorphic_casts.polymorphic_pointer_cast">polymorphic_pointer_cast</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="conversion/synopsis.html">Synopsis</a></span></dt>
<dt><span class="section"><a href="conversion/history.html">History</a></span></dt>
</dl>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="conversion.description"></a><a class="link" href="conversion.html#conversion.description" title="Description">Description</a>
</h2></div></div></div>
<p>
      The Conversion Library improves program safety and clarity by performing otherwise
      messy conversions. It includes cast-style function templates designed to complement
      the C++ Standard's built-in casts.
    </p>
<p>
      To reduce coupling, the Boost Conversion Library is supplied by several headers:
    </p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
          The <a href="../../boost/polymorphic_cast.hpp" target="_top">boost/polymorphic_cast.hpp</a>
          header provides <a class="link" href="conversion/polymorphic_casts.html#polymorphic_cast"><code class="computeroutput"><span class="identifier">polymorphic_cast</span><span class="special">&lt;&gt;</span></code></a> and <a class="link" href="conversion/polymorphic_casts.html#polymorphic_downcast"><code class="computeroutput"><span class="identifier">polymorphic_downcast</span><span class="special">&lt;&gt;</span></code></a>
          to perform safe casting between polymorphic types.
        </li>
<li class="listitem">
          The <a href="../../boost/polymorphic_pointer_cast.hpp" target="_top">boost/polymorphic_pointer_cast.hpp</a>
          header provides <a class="link" href="conversion/polymorphic_casts.html#polymorphic_pointer_cast"><code class="computeroutput"><span class="identifier">polymorphic_pointer_cast</span><span class="special">&lt;&gt;</span></code></a>
          and <a class="link" href="conversion/polymorphic_casts.html#polymorphic_pointer_cast"><code class="computeroutput"><span class="identifier">polymorphic_pointer_downcast</span><span class="special">&lt;&gt;</span></code></a>
        </li>
<li class="listitem">
          The <a href="../../boost/implicit_cast.hpp" target="_top">boost/implicit_cast.hpp</a>
          header provides <code class="computeroutput"><span class="identifier">implicit_cast</span><span class="special">&lt;&gt;</span></code> to perform implicit casts only
          (no down-cast, no void*-&gt;T*, no U-&gt;T if T has only explicit constructors
          for U).
        </li>
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